The present invention relates generally to agricultural combines. It relates particularly to the sieves.
An agricultural combine is a common and well-known machine for harvesting crop materials. Agricultural combines are available in various designs and models to perform the basic functions of reaping crop materials from a crop field, separating the grain from the non-grain crop materials, and discarding the non-grain crop materials back onto the crop field.
A typical combine includes a crop harvesting apparatus, or header, which reaps ripened crop plants from the crop field. The header then feeds the crop materials rearwardly to a threshing apparatus. One type of threshing apparatus that is well-known to those skilled in the art is a rotary thresher. In such a system, the crop materials are introduced to the front end of a rotor assembly, which is oriented longitudinally within the combine body with the rear end positioned angularly upwards from the front end. The crop materials are then threshed in the annular space between a rotating rotor and the inside of a rotor housing.
Along the exterior of the rotor is a series of rasp bars which repeatedly, but gently, strike the crop materials as they spiral through the annular space between the rotor and rotor housing. The rasp bars also cooperate with spiral vanes along the interior of the rotor housing so that the crop materials feed rearward through the rotor assembly. As the crop materials feed through the rotor assembly, the fine materials are separated from the course materials. Typically, the fine materials include grain, partial grain heads, and broken pieces of crop stalks; while the course materials include crop stalks, leaves, and empty grain heads. The unwanted course materials continue their rearward travel through the rotor assembly and are discharged out from the rotor assembly""s rear end. On the other hand, the fine materials pass through openings in the concave and grate which are positioned along the bottom side of the rotor housing.
The fine materials that pass from the rotor assembly are then further separated by a series of moving sieves. The sieves move in a constant back-and-forth motion, with the individual sieves generally moving in opposite directions to each other. Typically, a cleaning fan is used to blow forced air up through the sieve vanes so that the lighter fine materials are discharged from the rear end of the sieves. The heavier grain, on the other hand, passes through the sieve vanes and falls to the bottom of the combine body. The grain is then directed to an onboard grain bin through an augering system.
Generally, the drive system for the sieves is mechanically powered by the combine engine through a belt and pulley system. The combine engine usually also powers other moving components through either separate belts or, in some cases, through the same belt that drives the sieves. The drive ratio for the sieves is typically fixed by the diameters of the pulleys so that the moving speed of the sieves is directly proportional to the engine speed.
One problem with these belt drive systems is the durability of the belts. Frequently, the belts of a combine wear out and break during combining operations. This situation can be costly to the farmer, who is usually under pressure to harvest the crops during a limited optimal time period. Many times the belt drive systems in a combine become overly complex because of the large number of components that must be powered. Often, this system of multiple belts is so confusing that farmers find it difficult to quickly replace a broken belt with a new one.
Another problem is the inability to separately adjust the moving speed of the sieves. The moving speed of the sieves can have a significant impact on the performance of the sieves in separating grain from the fine materials. The optimal moving speed of the sieves can vary depending on a variety of factors, including the type of crop being harvested, the yield of the crop, and the particular combine settings being used. However, in the belt drive systems described, manufacturers usually choose a medium drive ratio that will provide a sieve moving speed that is considered acceptable for a broad range of conditions.
One problem encountered in developing new drive systems for the sieves is related to the high accelerations that can occur in the sieves. As previously explained, the sieves move in a constant, reciprocating motion, with about 265 back-and-forth cycles per minute being a common speed for the sieves. Thus, during the lifetime of a combine the sieves can experience as many as 60 million cycles. This constant cycling of the sieves can cause a variety of fatigue failures in the sieves, such as failures in the drive system joints and the welded seams of the side frames.
As is well-understood by those skilled in the art, changes in the travel speed, also referred to as accelerations, of the sieves contribute primarily to these fatigue failures. Therefore, in order to minimize stress on the sieves, the sieves preferably should travel smoothly between their backward and forward positions, with consistent or uniform speed changes. Of course, a certain amount of speed changes are necessary to accomplish the directional changes of the sieves. As a result of these directional speed changes, the drive shaft experiences a sinusoidal torque variation as it rotates and drives the sieves. Ideally, this sinusoidal torque curve should be smooth with a minimized amplitude.
Accelerations in the sieves, however, also occur due to other torque variations in the sieve""s drive system. Depending on the characteristics of the drive system, these torque and speed variations can become high frequency vibrations that contribute significantly to fatigue failures in the sieves. These vibrations can be seen in the sinusoidal torque curve of the drive shaft as a higher frequency noise that can greatly exaggerate the overall amplitude of torque variations caused by directional speed changes. In the belt drive systems previously described, variations in the drive shaft speed are minimized by the high inertia associated with these systems. These systems inherently have high inertia because the sieve""s drive system is mechanically connected to a number of other rotating components in the combine through belts and pulleys. The mechanical connection in these systems between several rotating components tends to have a flywheel effect that smoothes out the drive torque variations by minimizing drive shaft speed variations. However, in other drive systems where multiple belts and pulleys are not used, the inertia of the drive system can be relatively small. In these drive systems, therefore, torque and speed variations can result in greater accelerations in the sieves than usually occurs in belt drive systems.
Accordingly, it is an object of the invention to provide a drive system that minimizes accelerations in the sieves.
It is another object to provide a drive system including a flywheel which acts to minimize accelerations in the sieves.
It is a further object of the invention to provide a hydraulic motor for directly driving the sieves without using belts and pulleys.
The drive system for the sieves in the present invention includes a pivot member that is pivotally attached to one of the sieves and to a connecting arm. The connecting arm is attached at the other end to an oscillation mechanism which provides the sieves with a back-and-forth, reciprocating movement. The oscillation mechanism is driven by a drive shaft which is directly driven by a hydraulic motor. In order to minimize torque and speed variations in the drive system, a flywheel is provided.